The present invention relates generally to the processing of liquid streams. In preferred forms, the present invention relates to flowable polymeric streams, especially fiber-forming polymeric streams, formed of multiple pixels having different physical, visual and/or constituent properties, and to the methods and apparatus for forming the same.
It is oftentimes desirable to bring at least two liquid streams into intimate contact with one another. For example, in the processing of polymeric materials, especially melts of thermoplastic materials, it may be desirable to incorporate additives such as colorants, stabilizers, delusterants, flame retardants, fillers, antimicrobial agents, antistatic agents, optical brighteners, extenders, processing aids and other functional additives into polymeric host materials so as to engineer desired properties of the resulting blend. (See, for example, U.S. Pat. No. 5,834,089, the entire content of which is incorporated expressly hereinto by reference.)
It may also be desirable to bring at least two liquid reactant streams into intimate contact with each other so as to effect chemical reaction. For example, it may be desirable to continuously bring a polymerizable material into intimate contact with a catalyst and/or initiator so as to produce a polymeric material in a continuous manner. While relatively large-scale reactors are known for such purposes, it has more recently been suggested that relatively smaller scale plate reactors may be beneficial in some instances. (See in this regard, U.S. Pat. Nos. 5,534,328 and 5,843,385, the entire content of each being expressly incorporated hereinto by reference.)
In order to assist in the mixing of liquid streams, especially streams of polymeric materials or streams of chemical reactants, it has been proposed to use a series of stacked plates which define tortuous paths along which the mixture travels between the mixer inlet and outlet. (See in this regard, U.S. Pat. Nos. 5,137,369 and 5,851,562, the entire content of each being incorporated hereinto by reference). These static continuous mixers essentially require that at least two liquid streams be brought initially into contact with each other, with such an initial combination of liquid streams thereafter being subjected to a tortuous flow path to achieve the desired mixing.
While these conventional static continuous mixers are satisfactory for their intended purposes, some improvements are still desired in order to achieve truly homogeneous and/or substantially instantaneous blending of at least two different liquid streams. It is towards fulfilling such desires that the present invention is directed.
Broadly, the present invention contemplates that at least two different liquid streams are sub-divided into a dense plurality of individually separated parallel pixel substreams oriented in respective misregistered arrays. Therefore, an individual pixel of one of the liquid stream arrays will be surrounded by pixels of the other liquid stream array. These individual pixel arrays are then bought into contact with one another to form a multi-pixel liquid stream comprised of the misregistered pixel arrays of the two different liquid streams. The xe2x80x9cpixelatedxe2x80x9d liquid streamxe2x80x94that is, the liquid stream containing in cross-section the misregistered pixel arrays of the two different liquid streamsxe2x80x94may then be further processed. For example, the pixelated liquid stream may be subjected to further mixing by being directed along a tortuous flow path.
Since the pixelated liquid stream will exhibit, in cross-section, a dense plurality of individual mutually adjacent pixels formed of the two different liquid streams, there exists greater likelihood that a more homogenous and/or instantaneous blend will be achieved following further static mixing. However, even if a true homogenous blend is not achieved, the dense plurality of misregistered pixels will be visually perceived as being xe2x80x9cblendedxe2x80x9d. Such an attribute is important if the two liquid streams which are pixelated are differently colored and/or immiscible. Thus, the dense plurality of misregistered pixels of different colored liquids will exhibit a visually perceived color tone that is a combination of the coloration of each liquid stream, even though a true homogenous blend may not be achieved. Therefore, any further mixing of the pixels will only serve to enhance the visual appearance of the resulting combined liquid stream.
In particularly preferred forms of the invention, therefore, a series of plates is provided which fractionate the liquid streams into a geometric X-shaped patterns to form a dense plurality of 4(nxe2x88x921) number of pixels, where n is the number of plates employed. The xe2x80x9cfractal geometryxe2x80x9d of the X-design ensures that the channel path length, in the direction of liquid flow, is equivalent for any two pixel domains. This equivalence of channel length ensures uniform residence times, pressure drop and flow rates for any two pixel domains, which is especially critical for processing chemical reactant streams.
The present invention and the fractal geometry employed thereby increases the total interfacial area available at onset of mixing, but subdividing liquid streams into a dens plurality of substreams (pixels). When using X-shaped subdividing geometries, and assuming a constant, cumulative cross-sectional area of all pixel-forming apertures (and thereby constant flow velocities), the increased available surface area for each liquid flow will increase by a factor of 2n, wherein n is again the number of plates employed. Depending on the application, it might be desirable to decrease the velocity profile or increase the velocity profile by progressively increasing the total cross-sectional area of the apertures of decreasing the total cross-sectional area of the apertures, respectively. The resulting increase in the available surface area for each of the liquid streams by virtue of the dense plurality of misregistered pixels will thereby ensure substantially instantaneous mixing of two liquid streams once the individual respective pixels thereof come into contact with one another.
These and other aspects and advantages will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments which follows.